Qualcomm Technologies Inc., PMIC Round Robin ADC (RRADC)

PMIC RRADC provides an interface to the clients to read
the voltage, current and temperature for supported channels
such as battery ID, battery thermistor, die temperature,
charger temperature, USB_IN and DC_IN voltage and current.

Main node properties:

- compatible:
    Usage: required
    Value type: <string>
    Definition: Should contain "qcom,rradc".

- reg:
    Usage: required
    Value type: <prop-encoded-array>
    Definition: RRADC base address and length in the PMIC register map.

- #address-cells:
    Usage: required
    Value type: <u32>
    Definition: Must be one. Child node 'channel' property should define ADC
            channel number. For details about IIO bindings see:
            Documentation/devicetree/bindings/iio/iio-bindings.txt

- #size-cells:
    Usage: required
    Value type: <u32>
    Definition: Must be zero. For details about IIO bindings see:
            Documentation/devicetree/bindings/iio/iio-bindings.txt

- #io-channel-cells:
    Usage: required
    Value type: <u32>
    Definition: Must be one. For details about IIO bindings see:
            Documentation/devicetree/bindings/iio/iio-bindings.txt

IIO client nodes need to specify the RRADC channel number while requesting ADC reads.
The channel list supported by the RRADC driver is available in the enum rradc_channel_id
located at at drivers/iio/adc/qcom-rradc.c. Clients can use this index from the enum
as the channel number while requesting ADC reads.

Optional property:
- qcom,pmic-revid : Phandle pointing to the revision peripheral node. Use it to query the
		    PMIC fabrication ID for applying the appropriate temperature
		    compensation parameters.
Example:

	/* RRADC node */
	pmic_rradc: rradc@4500 {
		compatible = "qcom,rradc";
		reg = <0x4500 0x100>;
		#address-cells = <1>;
		#size-cells = <0>;
		#io-channel-cells = <1>;
	};

	/* IIO client node */
	charger {
		io-channels = <&pmic_rradc 0>;
		io-channel-names = "rradc_batt_id";
	};
